Memory Devices: Part I – Volatile Memories

This article illustrates the operation principles, circuit organization, performance and reliability issues of volatile memories, including the 6- and 4-transistors static RAM (SRAM), the 3- and 1-transistor dynamic RAM (DRAM), and the 10-transistor content addressable memory (CAM). First, the SRAM general features are discussed, including access time, packing density, and reliability issues. Also, a description of the basic cell topologies, cell array organization, and sense amplifier operation is provided. The treatment of DRAMs addresses the structural and functional properties of the one-transistor memory cell, the organization of the cell array, the structure and operation of the sense amplifier and the memory architecture. Finally, a short description of the structure and operation of associative memories is provided, as well as their basic application as a tag memory of set-associative caches.